Chevy Axle Ratio by VIN: Find the Factory Gear Ratio

Two identical-looking Silverados can behave like completely different trucks, and the reason often sits between the rear wheels. The factory axle ratio shapes acceleration, towing capacity, and highway RPM, and it is recorded against the VIN.

Chevrolet documents the rear axle in the build record as RPO codes, and axle codes generally begin with the letter G.

The ratio codes are specific. On many late-model GM trucks, GU6 identifies 3.42 gears, GT4 identifies 3.73 gears, and GT5 identifies 4.10 gears, though you should always confirm the meaning for your exact model year.

One famous G code is not a ratio at all. G80 is the automatic locking rear differential, a separate option that can ride alongside any of the gear sets.

To find yours, enter the 17-character VIN in the lookup tool on our home page. The site retrieves the window sticker or RPO build sheet, and the axle content is listed with the rest of the driveline.

The glove box label carries the same codes if the truck is in front of you, filed alphabetically among the Gs in the option grid.

Towing is the big reason to care. The same truck's maximum trailer rating can swing by thousands of pounds between the tall highway gearing and the short towing gearing.

The tradeoff is simple physics. Numerically higher ratios pull harder and tow more but spin more RPM on the highway, while numerically lower ratios cruise quieter and burn less fuel unloaded.

Shoppers should match the ratio to the job. Buying for a camper or a boat means hunting for the towing gears, while a commuter truck is happier with the highway set.

The code also helps you catch changes. If a previous owner regeared the truck, the recorded code and the actual axle no longer match, which a shop can verify quickly.

Parts depend on the code as well. Ring-and-pinion sets, bearings, and covers vary by axle, and the locking differential brings its own service considerations.

Ads love hard-to-check claims, and "tow package with 3.73s" is easy to type. Checking the record before you drive an hour is easier still.

Gearing is one leg of the towing setup. The full picture, from cooling to hitch equipment, is covered in Chevy Towing Package by VIN.

Truck-specific code reading, including the other Silverado equipment worth confirming, is in Chevrolet Silverado RPO Codes by VIN.

The axle ratio was chosen the day the truck was ordered, and it still defines what the truck is good at. Look it up first, and buy the truck whose gears match your trailer.